1. Field of the Invention
The present invention relates to a measurement apparatus which measures the transmittance distribution of an optical system to be measured, an exposure apparatus which incorporates the measurement apparatus, and a device manufacturing method of manufacturing a device using the exposure apparatus.
2. Description of the Related Art
FIG. 11 shows the arrangement of a measurement apparatus for measuring the transmittance distribution of an optical system to be measured. A method of measuring the intensity distribution of reference light will be explained first. An RS mirror (first spherical mirror) 13 for forming reference light is inserted between a condenser lens 5 and an optical system to be measured 6. A light beam emitted by a light source 1 is reflected by a half mirror 2, and reaches the condenser lens 5 via a beam expander 12 and mirrors 31 and 32. A light beam component which emerges from the condenser lens 5 and is reflected by the RS mirror 13 is transmitted through the half mirror 2, and forms a reference light intensity distribution Irsa(x, y) on the image sensing plane of an image sensor 9 via an imaging optical system 41.
A method of measuring the intensity distribution of test light will be explained next. A light beam transmitted through the optical system to be measured 6 is reflected by an RS mirror (second spherical mirror) 7 for forming test light. The light beam reflected by the RS mirror 7 is transmitted through the half mirror 2, and forms a test light intensity distribution Irsb(x, y) on the image sensing plane of the image sensor 9 via the imaging optical system 41.
On the basis of the reference light intensity distribution Irsa(x, y) and test light intensity distribution Irsb(x, y), the transmittance distribution of the optical system to be measured 6 is calculated. Letting I0 be the incident light intensity, Tsys(x, y) be the transmittance distribution of only the measurement apparatus, and Rrsa be the reflectance of the RS mirror 13, the reference light intensity distribution Irsa(x, y) is given by:Irsa(x, y)=Tsys(x, y)×Rrsa×I0
Likewise, letting Tlens(x, y) be the transmittance distribution of the optical system to be measured 6, and Rrsb be the reflectance of the RS mirror 7, the intensity distribution Irsb(x, y) of the test light as the light reflected by the RS mirror 7 is given by:Irsb(x, y)=Tsys(x, y)×(Tlens(x, y))2×Rrsb×I0
Hence, the transmittance distribution of the optical system to be measured 6 is given by:
                              Tlens          ⁡                      (                          x              ,              y                        )                          =                                            (                              Rrsa                /                Rrsb                            )                                      1              /              2                                ×                                    (                                                Irsa                  ⁡                                      (                                          x                      ,                      y                                        )                                                  /                                  Irsb                  ⁡                                      (                                          x                      ,                      y                                        )                                                              )                                      1              /              2                                                              =                  Const          ×                                    (                                                Irsb                  ⁡                                      (                                          x                      ,                      y                                        )                                                  /                                  Irsa                  ⁡                                      (                                          x                      ,                      y                                        )                                                              )                                      1              /              2                                          Note that Rrsa and Rrsb are measured by, e.g., a reflectance measurement device in advance.
Another method of measuring the transmittance of the optical system to be measured is also known (Japanese Patent Laid-Open No. 2005-158828).
The transmittance distribution of the optical system to be measured has conventionally been calculated assuming that the reflectances of both the RS mirrors 13 and 7 are uniform. However, if the reflectances of these two RS mirrors are nonuniform (i.e., their reflectances exhibit nonuniform distributions), the measurement result of the transmittance distribution often suffers from errors.